WO2022202195A1

WO2022202195A1 - Piezoelectric film

Info

Publication number: WO2022202195A1
Application number: PCT/JP2022/009174
Authority: WO
Inventors: 順平石田
Original assignee: 富士フイルム株式会社
Priority date: 2021-03-26
Filing date: 2022-03-03
Publication date: 2022-09-29
Also published as: CN116998168A; JPWO2022202195A1; KR20230136208A; US20230422626A1; TW202240944A; EP4319197A1

Abstract

Provided is a piezoelectric film having high piezoelectric performance. The piezoelectric film comprises: a piezoelectric layer comprising a polymer composite piezoelectric material containing piezoelectric particles in a matrix that comprises a polymer material; and electrode layers formed on the respective sides of the piezoelectric layer, wherein the circularity of the piezoelectric particles as observed in the cross-section in the thickness direction of the piezoelectric layer is 0.65-0.92.

Description

piezoelectric film

The present invention relates to piezoelectric films.

In response to the thinning of displays such as liquid crystal displays and organic EL displays, the speakers used in these thin displays are also required to be lighter and thinner. Furthermore, flexible displays are also required to be flexible in order to be integrated into flexible displays without impairing lightness and flexibility. As such a lightweight, thin and flexible speaker, it is considered to employ a sheet-like piezoelectric film having a property of expanding and contracting in response to an applied voltage.

It is also being considered to create a flexible speaker by attaching a flexible exciter to a flexible diaphragm. An exciter is an exciter that vibrates and emits sound by being attached to various articles in contact with them.

It has been proposed to use a flexible sheet-like piezoelectric film or a composite piezoelectric body containing piezoelectric particles in a matrix as an exciter.

For example, Patent Document 1 discloses a polymer composite piezoelectric material for electroacoustic conversion, in which piezoelectric particles are dispersed in a matrix made of a polymer material, wherein the piezoelectric particles have the general formula Pb (Zr _x Ti _1-x ) The main component is lead zirconate titanate represented by O ₃ , and a tetragonal crystal and a rhombohedral crystal are mixed in one piezoelectric particle, and laser scattering The median diameter (D ₅₀ ) of the piezoelectric particles measured by a particle size measuring device is 2 to 5 μm, and the piezoelectric particles having a particle diameter of 10 μm or more account for 5 to 30 vol % of the total piezoelectric particles, A polymer composite piezoelectric material for electroacoustic conversion is described in which piezoelectric particles having a particle diameter of 1 μm or less account for 10 vol % or less of all piezoelectric particles. Further, Patent Document 1 describes that electrode layers are provided on both sides of this polymer composite piezoelectric material to use it as an electroacoustic conversion film.

Japanese Patent No. 6043673

In such a piezoelectric film, there has been a demand for higher conversion efficiency between electrical energy and mechanical energy, that is, higher piezoelectric performance.

An object of the present invention is to solve the problems of the prior art, and to provide a piezoelectric film having high piezoelectric performance.

In order to solve such problems, the present invention has the following configurations.
[1] A piezoelectric layer made of a polymer composite piezoelectric material containing piezoelectric particles in a matrix containing a polymer material, and electrode layers formed on both sides of the piezoelectric layer,
A piezoelectric film in which the circularity of piezoelectric particles observed in a cross section in the thickness direction of the piezoelectric layer is 0.65 to 0.92.
[2] The piezoelectric film according to [1], wherein the piezoelectric particles have an average particle size of 0.5 μm to 5 μm.
[3] The piezoelectric film according to [1] or [2], wherein the piezoelectric particles have a circularity of 0.73 to 0.89.
[4] A laminated piezoelectric element obtained by laminating a plurality of layers of the piezoelectric film according to any one of [1] to [3].

According to the present invention, it is possible to provide a piezoelectric film having high piezoelectric performance.

1 is a diagram conceptually showing an example of a piezoelectric film of the present invention; FIG. It is a conceptual diagram for explaining an example of a method of manufacturing a piezoelectric film. It is a conceptual diagram for explaining an example of a method of manufacturing a piezoelectric film. It is a conceptual diagram for explaining an example of a method of manufacturing a piezoelectric film. It is a conceptual diagram for explaining an example of a method of manufacturing a piezoelectric film. 1 is a diagram conceptually showing an example of a piezoelectric element having a piezoelectric film of the present invention; FIG. FIG. 2 is a diagram conceptually showing another example of a piezoelectric element having the piezoelectric film of the present invention;

The piezoelectric film of the present invention will be described in detail below based on preferred embodiments shown in the accompanying drawings.

The description of the constituent elements described below may be made based on representative embodiments of the present invention, but the present invention is not limited to such embodiments.
In this specification, a numerical range represented by "-" means a range including the numerical values before and after "-" as lower and upper limits.

[Piezoelectric film]
The piezoelectric film of the present invention is
A piezoelectric layer made of a polymer composite piezoelectric material containing piezoelectric particles in a matrix containing a polymer material, and electrode layers formed on both sides of the piezoelectric layer,
In the piezoelectric film, the circularity of the piezoelectric particles observed in the cross section in the thickness direction of the piezoelectric layer is 0.65 to 0.92.

FIG. 1 conceptually shows an example of the piezoelectric film of the present invention.
As shown in FIG. 1, the piezoelectric film 10 includes a piezoelectric layer 20 which is a sheet-like material having piezoelectric properties, a first electrode layer 24 laminated on one surface of the piezoelectric layer 20, and a first electrode layer. 24 , a second electrode layer 26 laminated on the other surface of the piezoelectric layer 20 , and a second protective layer 30 laminated on the second electrode layer 26 .
The piezoelectric layer 20 is composed of a polymer composite piezoelectric body containing piezoelectric particles 36 in a matrix 34 containing a polymer material. Also, the first electrode layer 24 and the second electrode layer 26 are electrode layers in the present invention.
As will be described later, the piezoelectric film 10 (piezoelectric layer 20) is preferably polarized in the thickness direction.

Such a piezoelectric film 10 is used, for example, in various acoustic devices (acoustic equipment) such as speakers, microphones, and pickups used in musical instruments such as guitars to generate (reproduce) sounds by vibrating in response to electrical signals. It is also used to convert sound vibrations into electrical signals.
In addition, the piezoelectric film can also be used for pressure sensors, power generation elements, and the like.
Alternatively, the piezoelectric film can be used as an exciter that vibrates the article and emits sound by attaching it to various articles in contact therewith.

In the piezoelectric film 10, the second electrode layer 26 and the first electrode layer 24 form an electrode pair. That is, in the piezoelectric film 10 , both surfaces of the piezoelectric layer 20 are sandwiched between electrode pairs, that is, the first electrode layer 24 and the second electrode layer 26 , and this laminate is formed into the first protective layer 28 and the second protective layer 30 . It has a configuration sandwiched between.

Thus, in the piezoelectric film 10, the region sandwiched between the first electrode layer 24 and the second electrode layer 26 expands and contracts according to the applied voltage.

The first electrode layer 24 and the first protective layer 28, and the second electrode layer 26 and the second protective layer 30 are named according to the polarization direction of the piezoelectric layer 20. Therefore, the first electrode layer 24 and the second electrode layer 26 as well as the first protective layer 28 and the second protective layer 30 basically have the same configuration.

In addition to these layers, the piezoelectric film 10 may have, for example, an insulating layer or the like that covers the area where the piezoelectric layer 20 is exposed, such as the side surface, to prevent short circuits or the like.

In such a piezoelectric film 10, when a voltage is applied to the first electrode layer 24 and the second electrode layer 26, the piezoelectric particles 36 expand and contract in the polarization direction according to the applied voltage. As a result, the piezoelectric film 10 (piezoelectric layer 20) shrinks in the thickness direction. At the same time, due to the Poisson's ratio, the piezoelectric film 10 also expands and contracts in the in-plane direction. This expansion and contraction is about 0.01 to 0.1%. In addition, it expands and contracts isotropically in all directions in the in-plane direction.

The thickness of the piezoelectric layer 20 is preferably about 10-300 μm. Therefore, the expansion and contraction in the thickness direction is as small as about 0.3 μm at maximum.
On the other hand, the piezoelectric film 10, that is, the piezoelectric layer 20, has a size much larger than its thickness in the planar direction. Therefore, for example, if the length of the piezoelectric film 10 is 20 cm, the piezoelectric film 10 expands and contracts by about 0.2 mm at maximum due to voltage application.
Also, when pressure is applied to the piezoelectric film 10, the action of the piezoelectric particles 36 generates electric power.
By utilizing this, the piezoelectric film 10 can be used for various applications such as speakers, microphones, and pressure sensors, as described above.

Here, in the piezoelectric film 10 of the present invention, the circularity of the piezoelectric particles observed in the cross section in the thickness direction of the piezoelectric layer is 0.65 to 0.92.

The degree of circularity is expressed by 4π×(area)÷(perimeter) ² and represents the complexity of the shape. In the case of a perfect circle, the number is 1, and the more complicated the shape, the smaller the numerical value.

As described above, in a piezoelectric film using a piezoelectric layer composed of a polymer composite piezoelectric material containing piezoelectric particles in a matrix containing a polymer material, when a voltage is applied, the piezoelectric particles 36 expand and contract in the polarization direction. , the piezoelectric film 10 (piezoelectric layer 20) expands and contracts to convert electrical energy into mechanical energy.

Here, according to the study of the present inventor, when the piezoelectric particles 36 are close to a perfect circle, that is, when the degree of circularity is too close to 1, interactions between adjacent piezoelectric particles 36 occur point-to-point. Therefore, the force due to expansion and contraction is less likely to be transmitted, the mechanical energy of the piezoelectric particles 36 is less likely to be transmitted to the outside as the mechanical energy of the entire piezoelectric film, and the efficiency of converting electrical energy into mechanical energy (piezoelectric performance) is unlikely to be sufficiently high. I found out.

On the other hand, if the circularity of the piezoelectric particles 36 is too small, the shape of the piezoelectric particles 36 becomes too complicated. When the solvent is volatilized by using the piezoelectric layer, voids are generated and the filling rate of the piezoelectric layer is lowered. Therefore, it turned out that piezoelectric performance falls.

On the other hand, in the piezoelectric film of the present invention, by setting the circularity of the piezoelectric particles 36 to 0.92 or less, the piezoelectric particles 36 have a shape with moderate angles. Therefore, when a voltage is applied and the piezoelectric particles 36 expand and contract in the polarization direction, an interaction between the adjacent piezoelectric particles 36 occurs between the surfaces. The mechanical energy is easily transmitted to the outside as the mechanical energy of the entire piezoelectric film. Therefore, the efficiency of converting electrical energy into mechanical energy (piezoelectric performance) is higher.

In addition, in the piezoelectric film of the present invention, the circularity of the piezoelectric particles 36 is 0.65 or more, that is, the shape of the piezoelectric particles 36 is prevented from becoming too complicated, so that the piezoelectricity during the formation of the piezoelectric layer can be reduced. It is possible to suppress the formation of voids when the paint for the body layer is applied and then dried to volatilize the solvent. Therefore, it is possible to prevent the filling rate of the piezoelectric layer from decreasing, and the piezoelectric film can have high piezoelectric performance.

The circularity of the piezoelectric particles 36 is preferably 0.73 to 0.89, more preferably 0.80 to 0.88, in that the piezoelectric performance can be further improved.

An example of a method for measuring the circularity of piezoelectric particles will be described below.

A sample is cut from the piezoelectric film and cut in the thickness direction for cross-sectional observation. Cutting is carried out, for example, by attaching a histo knife blade width of 8 mm manufactured by Drukker to RM2265 manufactured by Leica Biosystems, setting the speed to 1 on the scale of the controller, and setting the meshing amount to 0.25 to 1 μm.

Next, using the cross-section processed sample, the cross section is observed by SEM (Scanning Electron Microscope). As the SEM, for example, S4800 manufactured by Hitachi High-Technologies Corporation can be used. Also, the sample may be conductively treated. For example, the sample may be conductively treated by platinum deposition and the working distance may be 2.8 mm.

Observation is an SE (secondary-electron) image, with the SE detector set to the upper (U), +BSE L. A. Set to 100. The conditions are acceleration voltage: 2 kV, probe current: high, the sharpest image is produced by focus adjustment and astigmatism adjustment, and automatic brightness adjustment (auto setting, brightness: 0, contrast :0).

The imaging magnification is such that the first electrode layer and the second electrode layer fit in one screen, and the width between both electrodes is half or more of the screen. Moreover, at that time, the two electrode layers are photographed so as to be horizontal to the bottom of the image.

The image obtained as described above is binarized. Specifically, first, the image analysis software WinROOF is used to linearly convert the density range of the original imaging data to the range of 0 (dark) to 255 (bright) gradation to enhance the contrast. Subsequently, the piezoelectric layer is selected in a rectangular shape so that the selected area is maximized in a range not including the first electrode layer and the second electrode layer, and the density range of 110 to 255 gradations is binarized.

Next, for the binarized part, in order to remove noise components such that only one pixel part is selected, and to separate particles that seem to be combined, the contraction process, which is an analysis function of WinROOF, is performed three times. Select and execute once, then select conditions for exclusive dilation processing three times and execute once, then execute circular separation processing once, and binarize the piezoelectric particles to be analyzed for circularity. got the image.

Subsequently, the circularity of each binarized piezoelectric particle is determined, and the arithmetic mean value thereof is determined. As described above, circularity is 4π×(area/(perimeter) ² ), where 0<circularity≦1. For SEM observation of the cross section, N5 visual field measurement is performed, the circularity is obtained for each measurement visual field, and the average value of the circularity values of the N5 visual fields is obtained, which is taken as the circularity of the piezoelectric particles in the piezoelectric film.

Here, the average particle size of the piezoelectric particles is preferably 0.5 μm to 5 μm, more preferably 0.7 μm to 4 μm, and even more preferably 0.9 μm to 3 μm, in order to further improve the piezoelectric performance.

For the average particle size of the piezoelectric particles, the equivalent circle diameter of each piezoelectric particle is obtained using the image binarized by the above method, and the average value is calculated. As for the average particle size, the N5 field of view of the cross section is also measured, and the average particle size is obtained for each measurement field, and is taken as the average particle size of the piezoelectric particles in the piezoelectric film.

<Piezoelectric layer>
The piezoelectric layer is a layer made of a polymeric composite piezoelectric body containing piezoelectric particles in a matrix containing a polymeric material, and is a layer that exhibits a piezoelectric effect that expands and contracts when a voltage is applied.

In the piezoelectric film 10, the piezoelectric layer 20, as a preferred embodiment, is composed of a polymeric composite piezoelectric body in which piezoelectric particles 36 are dispersed in a matrix 34 made of a polymeric material having viscoelasticity at room temperature. . In this specification, "ordinary temperature" refers to a temperature range of about 0 to 50.degree.

The piezoelectric film 10 of the present invention is suitably used for speakers having flexibility, such as speakers for flexible displays. Here, the polymeric composite piezoelectric material (piezoelectric layer 20) used in the flexible speaker preferably satisfies the following requirements. Therefore, it is preferable to use a polymeric material having viscoelasticity at room temperature as a material that satisfies the following requirements.

(i) Flexibility For example, when gripping a loosely bent state like a document like a newspaper or magazine for portable use, it is constantly subjected to a relatively slow and large bending deformation of several Hz or less from the outside. become. At this time, if the polymer composite piezoelectric material is hard, a correspondingly large bending stress is generated, and cracks occur at the interface between the polymer matrix and the piezoelectric particles, which may eventually lead to destruction. Therefore, the polymer composite piezoelectric body is required to have appropriate softness. Moreover, stress can be relieved if strain energy can be diffused to the outside as heat. Therefore, it is required that the loss tangent of the polymer composite piezoelectric material is appropriately large.

(ii) Sound quality Speakers vibrate piezoelectric particles at frequencies in the audio band of 20 Hz to 20 kHz, and the vibration energy causes the entire polymer composite piezoelectric material (piezoelectric film) to vibrate as one to reproduce sound. be. Therefore, the polymer composite piezoelectric body is required to have appropriate hardness in order to increase the transmission efficiency of vibration energy. In addition, if the frequency characteristics of the speaker are smooth, the amount of change in sound quality when the lowest resonance frequency changes as the curvature changes becomes small. Therefore, the loss tangent of the polymer composite piezoelectric body is required to be moderately large.

In summary, the polymer composite piezoelectric body is required to behave hard against vibrations of 20 Hz to 20 kHz and softly against vibrations of several Hz or less. Also, the loss tangent of the polymer composite piezoelectric body is required to be moderately large with respect to vibrations of all frequencies of 20 kHz or less.

In general, polymer solids have a viscoelastic relaxation mechanism, and as the temperature rises or the frequency decreases, large-scale molecular motion causes a decrease (relaxation) in the storage elastic modulus (Young's modulus) or a maximum loss elastic modulus (absorption). is observed as Among them, the relaxation caused by the micro-Brownian motion of the molecular chains in the amorphous region is called principal dispersion, and a very large relaxation phenomenon is observed. The temperature at which this primary dispersion occurs is the glass transition point (Tg), and the viscoelastic relaxation mechanism appears most prominently.

In the polymer composite piezoelectric body (piezoelectric layer 20), by using a polymer material having a glass transition point at room temperature, in other words, a polymer material having viscoelasticity at room temperature as a matrix, it is possible to suppress vibrations of 20 Hz to 20 kHz. This realizes a polymer composite piezoelectric material that is hard at first and behaves softly with respect to slow vibrations of several Hz or less. In particular, it is preferable to use a polymer material having a glass transition point at room temperature, ie, 0 to 50° C. at a frequency of 1 Hz, for the matrix of the polymer composite piezoelectric material, because this behavior is favorably expressed.

Various known materials can be used as polymer materials having viscoelasticity at room temperature. Preferably, a polymer material having a maximum value of 0.5 or more in loss tangent Tan δ at a frequency of 1 Hz in a dynamic viscoelasticity test at normal temperature, ie, 0 to 50° C., is used. As a result, when the polymer composite piezoelectric body is slowly bent by an external force, the stress concentration at the interface between the polymer matrix and the piezoelectric particles at the maximum bending moment is relaxed, and high flexibility can be expected.

In addition, the polymer material having viscoelasticity at room temperature preferably has a storage modulus (E') at a frequency of 1 Hz measured by dynamic viscoelasticity of 100 MPa or more at 0°C and 10 MPa or less at 50°C. As a result, the bending moment generated when the polymeric composite piezoelectric body is slowly bent by an external force can be reduced, and at the same time, it can behave rigidly against acoustic vibrations of 20 Hz to 20 kHz.

Further, it is more preferable that the polymer material having viscoelasticity at room temperature has a dielectric constant of 10 or more at 25°C. As a result, when a voltage is applied to the polymer composite piezoelectric material, a higher electric field is applied to the piezoelectric particles in the polymer matrix, so a large amount of deformation can be expected. On the other hand, however, in consideration of ensuring good moisture resistance and the like, it is also suitable for the polymer material to have a dielectric constant of 10 or less at 25°C.

Examples of polymeric materials having viscoelasticity at room temperature that meet these conditions include cyanoethylated polyvinyl alcohol (cyanoethylated PVA), polyvinyl acetate, polyvinylidene chloride core acrylonitrile, polystyrene-vinylpolyisoprene block copolymer, and polyvinylmethyl. Examples include ketones and polybutyl methacrylate. Commercially available products such as Hybler 5127 (manufactured by Kuraray Co., Ltd.) can also be suitably used as these polymer materials. Among them, as the polymer material, it is preferable to use a material having a cyanoethyl group, and it is particularly preferable to use cyanoethylated PVA. These polymer materials may be used singly or in combination (mixed).

The matrix 34 using such a polymer material having viscoelasticity at room temperature may use a plurality of polymer materials together, if necessary. That is, in addition to a viscoelastic material such as cyanoethylated PVA, other dielectric polymer materials may be added to the matrix 34 as necessary for the purpose of adjusting dielectric properties and mechanical properties.

Examples of dielectric polymer materials that can be added include polyvinylidene fluoride, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, and polyvinylidene fluoride-trifluoroethylene copolymer. and fluorine-based polymers such as polyvinylidene fluoride-tetrafluoroethylene copolymer, vinylidene cyanide-vinyl acetate copolymer, cyanoethylcellulose, cyanoethylhydroxysaccharose, cyanoethylhydroxycellulose, cyanoethylhydroxypullulan, cyanoethylmethacrylate, cyanoethylacrylate, cyanoethyl Cyano groups such as hydroxyethylcellulose, cyanoethylamylose, cyanoethylhydroxypropylcellulose, cyanoethyldihydroxypropylcellulose, cyanoethylhydroxypropylamylose, cyanoethylpolyacrylamide, cyanoethylpolyacrylate, cyanoethylpullulan, cyanoethylpolyhydroxymethylene, cyanoethylglycidolpullulan, cyanoethylsaccharose and cyanoethylsorbitol. Alternatively, polymers having cyanoethyl groups, and synthetic rubbers such as nitrile rubber and chloroprene rubber are exemplified. Among them, polymer materials having cyanoethyl groups are preferably used.

Further, in the matrix 34 of the piezoelectric layer 20, the dielectric polymer added in addition to the material having viscoelasticity at room temperature such as cyanoethylated PVA is not limited to one type, and plural types may be added. .

In addition to the dielectric polymer, the matrix 34 may include thermoplastic resins such as vinyl chloride resin, polyethylene, polystyrene, methacrylic resin, polybutene, and isobutylene, and phenolic resin for the purpose of adjusting the glass transition point Tg. , urea resins, melamine resins, alkyd resins, and thermosetting resins such as mica may be added. Furthermore, a tackifier such as rosin ester, rosin, terpene, terpene phenol, and petroleum resin may be added for the purpose of improving adhesiveness.

When adding a material other than a polymer material having viscoelasticity, such as cyanoethylated PVA, to the matrix 34 of the piezoelectric layer 20, the addition amount is not particularly limited, but the ratio of the material to the matrix 34 is 30% by mass or less. is preferable. As a result, the characteristics of the polymer material to be added can be expressed without impairing the viscoelastic relaxation mechanism in the matrix 34, so that the dielectric constant can be increased, the heat resistance can be improved, and the adhesion between the piezoelectric particles 36 and the electrode layer can be improved. favorable results can be obtained in terms of

The piezoelectric layer 20 is a polymeric composite piezoelectric body containing piezoelectric particles 36 in such a matrix 34 .

The piezoelectric particles 36 are made of ceramic particles having a perovskite or wurtzite crystal structure. Examples of ceramic particles constituting the piezoelectric particles 36 include lead zirconate titanate (PZT), lead zirconate lanthanate titanate (PLZT), barium titanate (BaTiO ₃ ), zinc oxide (ZnO), and A solid solution (BFBT) of barium titanate and bismuth ferrite (BiFe ₃ ) is exemplified. Only one kind of these piezoelectric particles 36 may be used, or a plurality of kinds thereof may be used together (mixed).

The particle size of the piezoelectric particles 36 is as described above.

Although the piezoelectric particles 36 in the piezoelectric layer 20 are uniformly and regularly dispersed in the matrix 34 in FIG. 1, the present invention is not limited to this. That is, the piezoelectric particles 36 in the piezoelectric layer 20 may be dispersed irregularly in the matrix 34 as long as they are preferably uniformly dispersed.

In the piezoelectric film 10, the quantitative ratio of the matrix 34 and the piezoelectric particles 36 in the piezoelectric layer 20 is not limited. It may be appropriately set according to the properties required for the piezoelectric film 10 . The volume fraction of the piezoelectric particles 36 in the piezoelectric layer 20 is preferably 30% to 80%, more preferably 50% or more, and therefore more preferably 50% to 80%. By setting the amount ratio between the matrix 34 and the piezoelectric particles 36 within the above range, favorable results can be obtained in terms of achieving both high piezoelectric characteristics and flexibility.

In the piezoelectric film 10 described above, as a preferred embodiment, the piezoelectric layer 20 is a polymer composite piezoelectric layer in which piezoelectric particles are dispersed in a viscoelastic matrix containing a polymer material having viscoelasticity at room temperature. However, the present invention is not limited to this, and as the piezoelectric layer, a polymer composite piezoelectric body in which piezoelectric particles are dispersed in a matrix containing a polymer material, which is used in known piezoelectric elements, is used. It is possible.

The thickness of the piezoelectric layer 20 is not particularly limited, and may be set as appropriate according to the application of the piezoelectric film 10, the properties required of the piezoelectric film 10, and the like. The thicker the piezoelectric layer 20 is, the more advantageous it is in terms of rigidity such as stiffness of the so-called sheet-like material, but the voltage (potential difference) required to expand and contract the piezoelectric film 10 by the same amount is increased. The thickness of the piezoelectric layer 20 is preferably 10 to 300 μm, more preferably 20 to 200 μm, even more preferably 30 to 150 μm. By setting the thickness of the piezoelectric layer 20 within the above range, favorable results can be obtained in terms of ensuring both rigidity and appropriate flexibility.

<Protective layer>
In the piezoelectric film 10, the first protective layer 28 and the second protective layer 30 cover the second electrode layer 26 and the first electrode layer 24, and provide the piezoelectric layer 20 with appropriate rigidity and mechanical strength. is responsible for That is, in the piezoelectric film 10, the piezoelectric layer 20 made up of the matrix 34 and the piezoelectric particles 36 exhibits excellent flexibility against slow bending deformation, but depending on the application, the rigidity may increase. and mechanical strength may be insufficient. The piezoelectric film 10 is provided with a first protective layer 28 and a second protective layer 30 to compensate.

There are no restrictions on the first protective layer 28 and the second protective layer 30, and various sheet materials can be used, and various resin films are suitable examples. Among them, polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polycarbonate (PC), polyphenylene sulfite (PPS), polymethyl methacrylate (PMMA), due to their excellent mechanical properties and heat resistance. ), polyetherimide (PEI), polyimide (PI), polyethylene naphthalate (PEN), triacetyl cellulose (TAC), cyclic olefin resins, and the like are preferably used.

The thicknesses of the first protective layer 28 and the second protective layer 30 are also not limited. Also, the thicknesses of the first protective layer 28 and the second protective layer 30 are basically the same, but may be different. Here, if the rigidity of the first protective layer 28 and the second protective layer 30 is too high, not only will the expansion and contraction of the piezoelectric layer 20 be restricted, but also the flexibility will be impaired. Therefore, the thinner the first protective layer 28 and the second protective layer 30, the better, except for cases where mechanical strength and good handling properties as a sheet-like article are required.

In the piezoelectric film 10, if the thickness of the first protective layer 28 and the second protective layer 30 is not more than twice the thickness of the piezoelectric layer 20, it is possible to ensure both rigidity and appropriate flexibility. favorable results can be obtained.
For example, when the thickness of the piezoelectric layer 20 is 50 μm and the first protective layer 28 and the second protective layer 30 are made of PET, the thicknesses of the first protective layer 28 and the second protective layer 30 are preferably 100 μm or less. 50 μm or less is more preferable, and 25 μm or less is even more preferable.

<Electrode layer>
In the piezoelectric film 10, a first electrode layer 24 is provided between the piezoelectric layer 20 and the first protective layer 28, and a second electrode layer 26 is provided between the piezoelectric layer 20 and the second protective layer 30. It is formed. The first electrode layer 24 and the second electrode layer 26 are provided for applying voltage to the piezoelectric layer 20 (piezoelectric film 10).

In the present invention, the materials for forming the first electrode layer 24 and the second electrode layer 26 are not limited, and various conductors can be used. Specifically, metals such as carbon, palladium, iron, tin, aluminum, nickel, platinum, gold, silver, copper, titanium, chromium and molybdenum, alloys thereof, laminates and composites of these metals and alloys, Also, indium tin oxide and the like are exemplified. Among them, copper, aluminum, gold, silver, platinum, and indium tin oxide are suitable examples of materials for the first electrode layer 24 and the second electrode layer 26 .

In addition, the method of forming the first electrode layer 24 and the second electrode layer 26 is not limited, and vapor phase deposition methods (vacuum film formation methods) such as vacuum deposition, ion-assisted deposition, and sputtering, film formation by plating, Alternatively, various known methods such as a method of adhering a foil made of the above material can be used.

Among them, a thin film of copper, aluminum, or the like formed by vacuum deposition is particularly preferably used as the first electrode layer 24 and the second electrode layer 26 because the flexibility of the piezoelectric film 10 can be ensured. be. Among them, a copper thin film formed by vacuum deposition is particularly preferably used.

The thicknesses of the first electrode layer 24 and the second electrode layer 26 are not limited. Also, the thicknesses of the first electrode layer 24 and the second electrode layer 26 are basically the same, but may be different.

Here, as with the first protective layer 28 and the second protective layer 30 described above, if the rigidity of the first electrode layer 24 and the second electrode layer 26 is too high, not only will the expansion and contraction of the piezoelectric layer 20 be restricted, Flexibility is also impaired. Therefore, from the viewpoint of flexibility and piezoelectric properties, the thinner the first electrode layer 24 and the second electrode layer 26 are, the better. That is, the first electrode layer 24 and the second electrode layer 26 are preferably thin film electrodes.

The thickness of the first electrode layer 24 and the second electrode layer 26 is thinner than that of the protective layer, preferably 0.05 μm to 10 μm, more preferably 0.05 μm to 5 μm, further preferably 0.08 μm to 3 μm, and 0.05 μm to 10 μm. 1 μm to 2 μm are particularly preferred.

Here, in the piezoelectric film 10, the product of the thickness of the first electrode layer 24 and the second electrode layer 26 and the Young's modulus is the product of the thickness of the first protective layer 28 and the second protective layer 30 and the Young's modulus. is preferable because the flexibility is not greatly impaired.

For example, the first protective layer 28 and the second protective layer 30 are made of PET (Young's modulus: about 6.2 GPa), and the first electrode layer 24 and the second electrode layer 26 are made of copper (Young's modulus: about 130 GPa). In this case, if the thickness of the first protective layer 28 and the second protective layer 30 is 25 μm, the thickness of the first electrode layer 24 and the second electrode layer 26 is preferably 1.2 μm or less, more preferably 0.3 μm or less. , it is preferably 0.1 μm or less.

As described above, the piezoelectric film 10 preferably includes the piezoelectric layer 20 formed by dispersing the piezoelectric particles 36 in the matrix 34 containing a polymer material having viscoelasticity at room temperature, the first electrode layer 24 and the second electrode layer 24 . It is sandwiched between the electrode layers 26, and further has a configuration in which this laminate is sandwiched between the first protective layer 28 and the second protective layer 30. As shown in FIG.

In such a piezoelectric film 10, the maximum value of the loss tangent (Tan δ) at a frequency of 1 Hz by dynamic viscoelasticity measurement preferably exists at room temperature, and the maximum value of 0.1 or more exists at room temperature. more preferred. As a result, even if the piezoelectric film 10 is subjected to a relatively slow and large bending deformation of several Hz or less from the outside, the strain energy can be effectively diffused to the outside as heat. It is possible to prevent cracks from occurring at the interface of

The piezoelectric film 10 preferably has a storage elastic modulus (E') at a frequency of 1 Hz measured by dynamic viscoelasticity measurement of 10 to 30 GPa at 0°C and 1 to 10 GPa at 50°C. Note that this condition applies to the piezoelectric layer 20 as well. This allows the piezoelectric film 10 to have a large frequency dispersion in the storage modulus (E'). That is, it can act hard against vibrations of 20 Hz to 20 kHz and soft against vibrations of several Hz or less.

In addition, the piezoelectric film 10 has a product of thickness and storage elastic modulus (E′) at a frequency of 1 Hz measured by dynamic viscoelasticity measurement of 1.0×10 ⁶ to 2.0×10 ⁶ N/m at 0° C. , 1.0×10 ⁵ to 1.0×10 ⁶ N/m at 50°C. Note that this condition applies to the piezoelectric layer 20 as well. As a result, the piezoelectric film 10 can have appropriate rigidity and mechanical strength within a range that does not impair flexibility and acoustic properties.

Furthermore, the piezoelectric film 10 preferably has a loss tangent (Tan δ) of 0.05 or more at 25° C. and a frequency of 1 kHz in a master curve obtained from dynamic viscoelasticity measurement. Note that this condition applies to the piezoelectric layer 20 as well. As a result, the frequency characteristics of the speaker using the piezoelectric film 10 are smoothed, and the amount of change in sound quality when the lowest resonance frequency _f0 changes as the curvature of the speaker changes can be reduced.

In the present invention, the storage elastic modulus (Young's modulus) and loss tangent of the piezoelectric film 10, piezoelectric layer 20, etc. may be measured by known methods. As an example, the dynamic viscoelasticity measuring device DMS6100 manufactured by SII Nanotechnology Co., Ltd. (manufactured by SII Nanotechnology Co., Ltd.) may be used for measurement.

As an example of the measurement conditions, the measurement frequency is 0.1 Hz to 20 Hz (0.1 Hz, 0.2 Hz, 0.5 Hz, 1 Hz, 2 Hz, 5 Hz, 10 Hz and 20 Hz), and the measurement temperature is -50 to 150 ° C. , a heating rate of 2° C./min (in a nitrogen atmosphere), a sample size of 40 mm×10 mm (including the clamping area), and a distance between chucks of 20 mm.

An example of a method for manufacturing the piezoelectric film 10 will be described below with reference to FIGS.

First, as shown in FIG. 2, a sheet-like object 10a having a first protective layer 28 and a first electrode layer 24 formed thereon is prepared. This sheet-like object 10a may be produced by forming a copper thin film or the like as the first electrode layer 24 on the surface of the first protective layer 28 by vacuum deposition, sputtering, plating, or the like.
When the first protective layer 28 is very thin and has poor handling properties, the first protective layer 28 with a separator (temporary support) may be used as necessary. As the separator, PET or the like having a thickness of 25 μm to 100 μm can be used. The separator may be removed after the second electrode layer 26 and the second protective layer 30 are thermally compressed and before laminating any member on the first protective layer 28 .

On the other hand, piezoelectric particles 36 are produced.
First, as starting materials, powders of Pb oxide, Zr oxide, and Ti oxide, which are the main components, are mixed in an amount ratio according to the overall composition of the piezoelectric particles to prepare a raw material powder. The raw material powder is prepared using a ball mill or the like.

This raw material mixed powder is placed in a crucible or the like and fired. From the viewpoint of adjusting the circularity to a suitable range, it is preferable that the firing temperature is about 700° C. to 900° C. and the firing time is about 3 hours to 6 hours.

After firing, if necessary, the produced piezoelectric particles are crushed. Crushing may be performed by a known method such as a method using a ball mill, a method of placing the powder on a mesh, and applying pressure from above to pass through the mesh. When using a ball mill, the pulverization time is preferably 3 to 40 hours.

Next, the paint that will become the piezoelectric layer is adjusted. A coating material is prepared by dissolving a polymeric material as a matrix material in an organic solvent, adding piezoelectric particles 36, and stirring and dispersing the mixture.

Here, in the present invention, in order to set the circularity of the piezoelectric particles in the range of 0.65 to 0.92, as shown in FIG. Stirring is preferably performed using two types of stirring blades, the blade 82 and the anchor type stirring blade 84 .

The propeller-type stirring blade 82 is a general propeller-type stirring blade. Also, the anchor-type stirring blade 84 is a general anchor-type stirring blade.

In the past, a propeller type stirring blade (propeller mixer) was used for stirring. Since it is done with a mixer, it is necessary to increase the rotation speed of the propeller mixer. As a result, a high shearing force acts, and the piezoelectric particles are excessively pulverized, resulting in chipping of the piezoelectric particles to remove the corners and make them round. Therefore, the piezoelectric particles have a shape close to a perfect circle. That is, the degree of circularity increases. On the other hand, when the rotation speed of the propeller mixer is low, the piezoelectric particles settle, so that the piezoelectric particles are not sufficiently dispersed and are not easily pulverized. is likely to become lower.

On the other hand, in the stirring using the propeller-type stirring blades 82 and the anchor-type stirring blades 84 at the same time, the stirring by the anchor-type stirring blades 84 having a shape along the bottom and side surfaces of the stirring tank 80 is mainly piezoelectric. Prevent sedimentation of body particles. On the other hand, the stirring by the propeller-type stirring blade 82 mainly promotes the diffusion of the piezoelectric particles.

That is, by preventing sedimentation by stirring with the anchor-type stirring blades 84, the piezoelectric particles can be sufficiently dispersed even when the rotation speed of the propeller-type stirring blades 82 is low. Therefore, by adjusting the number of revolutions of each of the anchor-type stirring blade 84 and the propeller-type stirring blade 82, an appropriate shearing force is applied to appropriately pulverize the piezoelectric particles, thereby increasing the circularity of the piezoelectric particles. can be adjusted.

The number of revolutions of the anchor-type stirring blade 84 and the propeller-type stirring blade 82 can be appropriately set according to the viscosity of the paint, the volume fraction of the piezoelectric particles, the size and shape of each stirring blade, the size of the stirring tank, and the like. good.

The number of revolutions of the anchor-type stirring blade 84 may be a number of revolutions at which the function of preventing the sedimentation of the piezoelectric particles can be obtained.

The rotation speed of the propeller-type stirring blade 82 can obtain the function of diffusing the piezoelectric particles, and may be set to a rotation speed that appropriately pulverizes the piezoelectric particles. 400 rpm to 800 rpm is more preferred.

After the sheet-like material 10a is prepared and the paint is prepared, the paint is cast (applied) on the sheet-like material 10a and dried by evaporating the organic solvent. As a result, as shown in FIG. 4, the laminate 10b having the first electrode layer 24 on the first protective layer 28 and the piezoelectric layer 20 on the first electrode layer 24 is produced. .

There are no restrictions on the method of casting this paint, and all known methods (coating devices) such as slide coaters and doctor knives can be used.

As described above, in the piezoelectric film 10, the matrix 34 may be added with a dielectric polymer material other than a viscoelastic material such as cyanoethylated PVA.
When these polymeric materials are added to the matrix 34, the polymeric materials to be added to the coating material described above may be dissolved.

After manufacturing the laminate 10b having the first electrode layer 24 on the first protective layer 28 and the piezoelectric layer 20 formed on the first electrode layer 24, the polarization of the piezoelectric layer 20 is preferably Perform processing (polling). The method of polarization treatment of the piezoelectric layer 20 is not limited, and known methods can be used.

Before this polarization treatment, the surface of the piezoelectric layer 20 may be smoothed using a heating roller or the like, or subjected to a calendering treatment. By performing this calendering process, the thermocompression bonding process, which will be described later, can be performed smoothly.

While the piezoelectric layer 20 of the laminate 10b is subjected to polarization treatment in this way, the sheet-like object 10c in which the second electrode layer 26 is formed on the second protective layer 30 is prepared. This sheet-like object 10c may be produced by forming a copper thin film or the like as the second electrode layer 26 on the surface of the second protective layer 30 by vacuum deposition, sputtering, plating, or the like.

Next, as shown in FIG. 5, the second electrode layer 26 is directed toward the piezoelectric layer 20, and the sheet-like object 10c is laminated on the laminate 10b for which the polarization treatment of the piezoelectric layer 20 has been completed.
Further, the laminate of the laminate 10b and the sheet-like material 10c is thermocompression-bonded by a heating press device, a pair of heating rollers or the like while sandwiching the second protective layer 30 and the first protective layer 28 to form a piezoelectric film. 10 is made. Alternatively, it may be cut into a desired shape after thermocompression bonding.

It should be noted that the processes up to this point can also be carried out while transporting a sheet that is not in the form of a sheet, but in the form of a web, that is, a sheet wound up in a long continuous state. Both the laminate 10b and the sheet-like material 10c can be web-like and can be thermocompressed as described above. In that case, the piezoelectric film 10 is produced in web form at this point.

Furthermore, an adhesive layer may be provided when laminating the laminate 10b and the sheet-like material 10c. For example, an adhesive layer may be provided on the surface of the second electrode layer 26 of the sheet 10c. The most preferred adhesive layer is the same material as matrix 34 . The same material may be applied on the piezoelectric layer 20, or may be applied on the surface of the second electrode layer 26 and attached.

Here, general piezoelectric films made of polymer materials such as PVDF (PolyVinylidene DiFluoride) have in-plane anisotropy in piezoelectric properties, and anisotropy in the amount of expansion and contraction in the plane direction when a voltage is applied. There is

On the other hand, the piezoelectric layer of the piezoelectric film of the present invention, which is composed of a polymer composite piezoelectric material containing piezoelectric particles in a matrix containing a polymer material, has no in-plane anisotropy in the piezoelectric properties, and has no in-plane anisotropy. In the inner direction, it expands and contracts isotropically in all directions. According to such a piezoelectric film 10 that expands and contracts isotropically two-dimensionally, it can vibrate with a larger force than a general piezoelectric film such as PVDF that expands and contracts greatly only in one direction. And it can produce beautiful sounds.

Further, for example, by attaching the piezoelectric film of the present invention to a flexible display device such as a flexible organic electroluminescence display and a flexible liquid crystal display, the film can be used as a speaker of the display device. is also possible.

Further, for example, when the piezoelectric film 10 is used for a speaker, the film-shaped piezoelectric film 10 itself may vibrate to generate sound. Alternatively, the piezoelectric film 10 may be attached to a diaphragm and used as an exciter that vibrates the diaphragm by the vibration of the piezoelectric film 10 to generate sound.

In addition, the piezoelectric film 10 of the present invention works well as a piezoelectric vibrating element for vibrating an object to be vibrated, such as a diaphragm, by forming a laminated piezoelectric element in which a plurality of sheets are laminated.

As an example, as shown in FIG. 6, a laminated piezoelectric element 50 in which piezoelectric films 10 are laminated is attached to a diaphragm 12, and a speaker that outputs sound by vibrating the diaphragm 12 with the laminated body of the piezoelectric films 10 is produced. good too. That is, in this case, the laminate of the piezoelectric films 10 acts as a so-called exciter that outputs sound by vibrating the diaphragm 12 .

By applying a drive voltage to the laminated piezoelectric element 50 in which the piezoelectric films 10 are laminated, the individual piezoelectric films 10 expand and contract in the plane direction, and the expansion and contraction of each piezoelectric film 10 causes the entire laminate of the piezoelectric films 10 to expand in the plane direction. Stretch. Due to the expansion and contraction of the laminated piezoelectric element 50 in the planar direction, the diaphragm 12 to which the laminate is adhered bends, and as a result, the diaphragm 12 vibrates in the thickness direction. This vibration in the thickness direction causes the diaphragm 12 to generate sound. The diaphragm 12 vibrates according to the magnitude of the driving voltage applied to the piezoelectric film 10 and generates sound according to the driving voltage applied to the piezoelectric film 10 . Therefore, at this time, the piezoelectric film 10 itself does not output sound.

Even if the rigidity of each piezoelectric film 10 is low and the expansion/contraction force is small, the laminated piezoelectric element 50 in which the piezoelectric films 10 are laminated has high rigidity, and the expansion/contraction force of the laminate as a whole is large. As a result, the laminated piezoelectric element 50 in which the piezoelectric film 10 is laminated can sufficiently bend the diaphragm 12 with a large force even if the diaphragm has a certain degree of rigidity, and the diaphragm 12 is bent in the thickness direction. By vibrating sufficiently, the diaphragm 12 can generate sound.

In the laminated piezoelectric element 50 in which the piezoelectric films 10 are laminated, the number of laminated piezoelectric films 10 is not limited. You can set it. It should be noted that a single piezoelectric film 10 can be used as a similar exciter (piezoelectric vibrating element) as long as it has sufficient stretching force.

The vibration plate 12 that is vibrated by the laminated piezoelectric element 50 in which the piezoelectric film 10 is laminated is also not limited, and various sheet-like objects (plate-like objects, films) can be used. Examples include resin films such as polyethylene terephthalate (PET), foamed plastics such as polystyrene foam, paper materials such as cardboard, glass plates, and wood. Furthermore, various devices such as display devices such as organic electroluminescence displays and liquid crystal displays may be used as the diaphragm as long as they can be bent sufficiently.

In the laminated piezoelectric element 50 in which the piezoelectric films 10 are laminated, it is preferable that the adjacent piezoelectric films 10 are adhered with the adhesion layer 19 (adhesive). Also, the laminated piezoelectric element 50 and the diaphragm 12 are preferably attached with the adhesive layer 16 .

There are no restrictions on the adhesive layer, and various types of materials that can be used to attach objects to be attached can be used. Therefore, the sticking layer may be made of a pressure-sensitive adhesive or an adhesive. Preferably, an adhesive layer is used which, after application, results in a solid and hard adhesive layer. The above points are the same for a laminated body formed by folding a long piezoelectric film 10 described later.

In the laminated piezoelectric element 50 in which the piezoelectric films 10 are laminated, the polarization direction of each laminated piezoelectric film 10 is not limited. The piezoelectric film 10 of the present invention is preferably polarized in the thickness direction. The polarization direction of the piezoelectric film 10 referred to here is the polarization direction in the thickness direction. Therefore, in the laminated piezoelectric element 50, all the piezoelectric films 10 may have the same polarization direction, or there may be piezoelectric films having different polarization directions.

In the laminated piezoelectric element 50 in which the piezoelectric films 10 are laminated, the piezoelectric films 10 are preferably laminated so that the polarization directions of the adjacent piezoelectric films 10 are opposite to each other. In the piezoelectric film 10 , the polarity of the voltage applied to the piezoelectric layer 20 depends on the polarization direction of the piezoelectric layer 20 . Therefore, regardless of whether the polarization direction is from the second electrode layer 26 to the first electrode layer 24 or from the first electrode layer 24 to the second electrode layer 26, the second electrode is The polarity of layer 26 and the polarity of first electrode layer 24 are made the same. Therefore, by reversing the polarization directions of the adjacent piezoelectric films 10, even if the electrode layers of the adjacent piezoelectric films 10 are in contact with each other, the contacting electrode layers have the same polarity, so a short circuit occurs. there is no fear of

As shown in FIG. 7, the laminated piezoelectric element in which the piezoelectric films 10 are laminated may have a structure in which a plurality of piezoelectric films 10 are laminated by folding the piezoelectric film 10L one or more times, preferably a plurality of times. The laminated piezoelectric element 56 in which the piezoelectric film 10 is folded and laminated has the following advantages.

In a laminate in which a plurality of cut sheet-like piezoelectric films 10 are laminated, it is necessary to connect the second electrode layer 26 and the first electrode layer 24 to the drive power source for each piezoelectric film. On the other hand, in the structure in which the long piezoelectric film 10L is folded and laminated, the laminated piezoelectric element 56 can be configured with only one long piezoelectric film 10L. Therefore, in the configuration in which the long piezoelectric film 10L is folded and laminated, only one power supply is required for applying the driving voltage, and the electrode from the piezoelectric film 10L can be led out at one place. Furthermore, in the structure in which the long piezoelectric films 10L are folded and laminated, the polarization directions of adjacent piezoelectric films are inevitably opposite to each other.

Regarding such a laminated piezoelectric element in which piezoelectric films having electrode layers and protective layers provided on both sides of a piezoelectric layer made of a polymer composite piezoelectric body are laminated, International Publication No. 2020/095812 and International Publication No. 2020/ 179353 and the like.

Although the piezoelectric film of the present invention has been described in detail above, the present invention is not limited to the above examples, and various improvements and modifications may be made without departing from the gist of the present invention. is.

Hereinafter, the present invention will be described in more detail by giving specific examples of the present invention. The present invention is not limited to this example, and the materials, amounts used, proportions, processing details, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the gist of the present invention. can.

[Example 1]

Sheets

10a and 10c were prepared by forming a copper thin film with a thickness of 100 nm on a PET film with a thickness of 4 μm by sputtering. That is, in this example, the first electrode layer 24 and the second electrode layer 26 are copper thin films with a thickness of 100 nm, and the first protective layer 28 and the second protective layer 30 are PET films with a thickness of 4 μm.
In addition, in order to obtain good handling during the process, a PET film with a separator (temporary support PET) having a thickness of 50 μm was used, and the separator of each protective layer was removed after the sheet-like material 10c was thermocompressed. rice field.

On the other hand, powders of Pb oxide, Zr oxide and Ti oxide, which are the main components, were mixed as starting materials.

Next, the raw material mixed powder obtained was fired at 700 to 800°C. After the firing, dry pulverization was performed in a ball mill at a ball diameter of 1 mm, a ball filling rate of 30%, and a rotation speed of 60 rpm for 10 hours to obtain piezoelectric particles 36 .

Next, cyanoethylated PVA (CR-V, manufactured by Shin-Etsu Chemical Co., Ltd.) was dissolved in methyl ethyl ketone (MEK). After that, the piezoelectric particles 36 obtained above are added to this solution in the following composition ratio, and stirred using the propeller-type stirring blade 82 and the anchor-type stirring blade 84 to form the piezoelectric layer 20 . Paint 20a was prepared.
・PZT particles・・・・・・・・・・300 parts by mass ・Cyanoethylated PVA・・・・・・・・15 parts by mass ・MEK・・・・・・・・・・・・85 parts by mass

The size of the stirring tank 80 was Φ400 mm×height 600 mm. Propeller-type stirring blades 82 used propeller blades with a blade diameter of 100 mm (6-pitch disk turbine manufactured by Satake Chemical Machinery Co., Ltd.). As the anchor type stirring blade 84, an anchor paddle manufactured by Satake Chemical Machinery Co., Ltd. and having a blade diameter of 350 mm was used. The rotation speed of the propeller-type stirring blade 82 was set to 200 rpm. The rotation speed of the anchor-type stirring blade 84 was set to 60 rpm.

On the first electrode layer 24 (copper thin film) of the sheet 10a previously prepared, the previously prepared paint 20a for forming the piezoelectric layer 20 was applied using a slide coater. In addition, the paint was applied so that the thickness of the coating film after drying was 25 μm.

Next, the sheet material 10a coated with paint was placed on a hot plate at 120°C, and the coating film was dried by heating. MEK was thereby evaporated to form a laminate 10b.

next. A sheet 10c was laminated on the laminated body 10b with the second electrode layer 26 (copper thin film side) side facing the piezoelectric layer 20, and was thermocompression bonded at 120.degree.
Thus, the piezoelectric film 10 having the first protective layer 28, the first electrode layer 24, the piezoelectric layer 20, the second electrode layer 26 and the second protective layer 30 in this order was produced.

The produced piezoelectric film 10 is cut in the thickness direction by the above-described method, and an image of the cross section is obtained with an SEM. It was obtained as an average value. Table 1 shows the measurement results.

[Examples 2 to 5]
Piezoelectric films were produced in the same manner as in Example 1, except that the rotation speeds of the propeller-type stirring blades 82 were set to 300 rpm, 500 rpm, 700 rpm, and 1000 rpm, respectively. The circularity and average particle size of the piezoelectric particles of the produced piezoelectric film were measured in the same manner as described above.

[Examples 6 to 12]
Piezoelectric films were produced in the same manner as in Example 3, except that the dry pulverization time in the ball mill was 0.5 hours, 1 hour, 3 hours, 5 hours, 20 hours, 40 hours and 100 hours. The circularity and average particle size of the piezoelectric particles of the produced piezoelectric film were measured in the same manner as described above.

[Comparative Example 1]
A piezoelectric film was produced in the same manner as in Example 1, except that the number of rotations of the propeller-type stirring blades 82 was set to 2000 rpm. The circularity and average particle size of the piezoelectric particles of the produced piezoelectric film were measured in the same manner as described above.

[Comparative Examples 2-3]
Piezoelectric films were produced in the same manner as in Example 1, except that the anchor-type stirring blades 84 were not used and the rotation speeds of the propeller-type stirring blades 82 were set to 2000 rpm and 1000 rpm, respectively. The circularity and average particle size of the piezoelectric particles of the produced piezoelectric film were measured in the same manner as described above.

[Comparative Examples 4-5]
Piezoelectric films were produced in the same manner as in Example 1, except that the propeller-type stirring blades 82 were not used and the rotation speeds of the anchor-type stirring blades 84 were set to 60 rpm and 20 rpm, respectively. The circularity and average particle size of the piezoelectric particles of the produced piezoelectric film were measured in the same manner as described above.

[evaluation]
First, a rectangular test piece of 210×300 mm (A4 size) was cut out from the produced piezoelectric film. After placing the cut-out piezoelectric film on a case with an opening of 210 x 300 mm containing glass wool, the peripheral portion was pressed with a frame, and the piezoelectric film was given appropriate tension and curvature to form a piezoelectric speaker. made. The depth of the case was 9 mm, the density of the glass wool was 32 kg/m ³ , and the thickness before assembly was 25 mm.

A sine wave of 1 kHz was input as an input signal to the manufactured piezoelectric speaker through a power amplifier, and the sound pressure was measured with a microphone placed at a distance of 60 cm from the center of the speaker.
Table 1 shows the results.

From Table 1, it can be seen that the piezoelectric film of the present invention has higher sound pressure and higher piezoelectric performance than the comparative examples.
In Comparative Examples 1 and 2, the number of revolutions of the propeller-type stirring blades during the dispersion of the paint was too high, so that the piezoelectric particles were excessively pulverized and the circularity of the piezoelectric particles increased. I can think. It is thought that when the degree of circularity is too high, the interaction between adjacent piezoelectric particles becomes difficult to propagate, resulting in a low sound pressure.
In Comparative Example 3, the rotation speed of the propeller-type stirring blade was low and there was no stirring by the anchor-type stirring blade, so the piezoelectric particles settled down and the piezoelectric particles were not sufficiently pulverized. presumably decreased. If the degree of circularity is too low in this way, voids are formed and the filling rate of the piezoelectric layer is lowered, which is thought to lower the sound pressure.
In Comparative Examples 4 and 5, the piezoelectric particles were not sufficiently pulverized because there was no stirring by the propeller-type stirring blade, and the circularity of the piezoelectric particles was considered to be low. If the degree of circularity is too low in this way, voids are formed and the filling rate of the piezoelectric layer is lowered, which is thought to lower the sound pressure.

From the comparison of Examples 1 to 5, it can be seen that the circularity of the piezoelectric particles is preferably 0.73 to 0.89.
Also, from the comparison of Examples 3 and 6 to 12, it can be seen that the average particle size of the piezoelectric particles is preferably 0.5 μm to 5 μm.
From the above results, the effect of the present invention is clear.

The piezoelectric film of the present invention can be used, for example, in various sensors such as sound wave sensors, ultrasonic sensors, pressure sensors, tactile sensors, strain sensors and vibration sensors (especially for infrastructure inspection such as crack detection and manufacturing site inspection such as foreign matter contamination detection). useful), acoustic devices such as microphones, pickups, speakers and exciters (specific applications include noise cancellers (used in cars, trains, airplanes, robots, etc.), artificial vocal cords, buzzers for preventing insects and vermin from entering , furniture, wallpaper, photographs, helmets, goggles, headrests, signage, robots, etc.), automobiles, smartphones, smart watches, haptics used for games, etc. Ultrasonic probes and hydrophones Acoustic transducers, actuators used for water drop adhesion prevention, transport, agitation, dispersion, polishing, etc., dampers used in containers, vehicles, buildings, sports equipment such as skis and rackets, and roads, floors, mattresses, and chairs , shoes, tires, wheels, and personal computer keyboards.

Reference Signs List

10, 10L

piezoelectric film

10a, 10c sheet-like material 10b laminate 12

diaphragm

16, 19 adhesive layer 20 piezoelectric layer 24 first electrode layer 26 second electrode layer 28 first protective layer 30 second protective layer 34 matrix 36

Piezoelectric particles

50, 56 Laminated piezoelectric element 58 Core rod 80 Stirring tank 82 Propeller type stirring blade 84 Anchor type stirring blade

Claims

A piezoelectric layer made of a polymer composite piezoelectric material containing piezoelectric particles in a matrix containing a polymer material, and electrode layers formed on both sides of the piezoelectric layer,
A piezoelectric film, wherein the circularity of the piezoelectric particles observed in a cross section in the thickness direction of the piezoelectric layer is 0.65 to 0.92.
The piezoelectric film according to claim 1, wherein the piezoelectric particles have an average particle size of 0.5 µm to 5 µm.
The piezoelectric film according to claim 1 or 2, wherein the piezoelectric particles have a circularity of 0.73 to 0.89.
A laminated piezoelectric element obtained by laminating a plurality of layers of the piezoelectric film according to any one of claims 1 to 3.